Methods and apparatus for forming a glass ribbon

ABSTRACT

A roll forming apparatus includes at least one forming roll being spaced from a forming body to define a gap. The forming roll includes a working zone portion having a working zone surface with a length extending along a rotation axis of the forming roll and a thermal resistance boundary extending at an acute angle relative to the rotation axis. In further examples, methods include the step of feeding a stream of molten glass through the gap to form a glass ribbon including a formed thickness. The thermal resistance boundary facilitates substantial uniform radial expansion of the working zone surface relative to the rotation axis across the length of the working zone surface in response to heating of the working zone portion by the molten glass.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119 toU.S. Provisional Application Ser. No. 61/858,295, filed on Jul. 25,2013, the content of which is relied upon and incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to methods and apparatus forforming a glass ribbon and, more particularly, to a methods andapparatus for forming a glass ribbon with at least one forming roll anda forming body spaced to define a glass forming gap.

BACKGROUND

Rolled sheet glass is typically formed using a pair of forming rolls.However, conventional glass roll forming machines that employ formingrolls typically produce glass ribbon that does not have a high precisionof dimensional uniformity (e.g. thickness uniformity within +/−0.025 mm)and are unable to form thin glass ribbon below 2-3 mm in thickness. Onefactor that contributes to this lack of precise thickness control is thenon-uniform radial thermal expansion of the forming rolls that are beingheated by the stream of molten glass that is formed into the glassribbon.

FIG. 1 illustrates a schematic view of two conventional forming rolls101, 103 that are not necessarily drawn to scale for clarity. As show,the forming rolls are spaced from each other to define a glass forminggap 105 for receiving a stream of molten glass 107. The forming rolls101, 103 may expand radially in a non-uniform manner due to heating fromthe stream of molten glass 107 (which may be about 1000° C. or higher).For example, as indicated by dashed lines 109 a, 109 b, heating of theforming rolls 101, 103 by the stream of molten glass 107 can cause aworking zone surface of each of the forming rolls to expand radiallyfrom the corresponding rotation axis in a non-uniform manner across thelength of the working zone surface. The non-uniform radial expansionoccurs since the central portions of the forming rolls 101, 103 arebeing raised to a higher temperature than the corresponding end portionsof the forming rolls 101, 103. Due to the non-uniform radial expansion,glass ribbon formed by the forming rolls may consequently have arelatively thin central portion when compared to the outer oppositeedges of the glass ribbon.

There is a desire to provide forming rolls that may be used to form aglass ribbon with a thickness profile that is not substantially varieddue to radial expansion of the forming rolls when heated.

SUMMARY

The following presents a simplified summary of the disclosure in orderto provide a basic understanding of some example aspects described inthe detailed description.

In a first aspect, a roll forming apparatus includes a glass feed devicefor supplying a stream of molten glass and at least one forming rollbeing spaced from a forming body to define a glass forming gap betweenthe forming roll and the forming body for receiving the stream of moltenglass to form a glass ribbon having a formed thickness. The forming rollincludes a working zone portion that comprises a working zone surfacefor engaging the stream of molten glass. The working zone surfaceincludes a length extending along a rotation axis of the forming roll.The forming roll further includes a thermal resistance boundaryextending at an acute angle relative to the rotation axis of the formingroll.

In one example of the first aspect, the thermal resistance boundary isconfigured such that the working zone surface expands radially from therotation axis in a substantially uniform manner across the length of theworking zone surface as a temperature of the working zone portion isincreased from a first temperature to a second temperature.

In another example of the first aspect, the thermal resistance boundarycomprises a frustoconical end surface of the working zone portion.

In yet another example of the first aspect, the thermal resistanceboundary comprises a plurality of bores spaced radially about therotation axis of the forming roll.

In still yet another example of the first aspect, the thermal resistanceboundary comprises a frustoconical groove defined in the forming roll.For example, the frustoconical groove can be provided with one or morestrength elements positioned within the groove.

In yet another example of the first aspect, the forming roll includes acooling passage configured to provide fluid cooling to the forming roll.

In still yet another example of the first aspect, the roll formingapparatus further comprises at least one pair of gap rings, wherein theforming roll and forming body are spaced by the pair of gap rings todefine the glass forming gap.

In another example of the first aspect, the pair of gap rings aremounted to the working zone portion of the forming roll.

In yet another example of the first aspect, the acute angle is fromabout 30° to about 60°.

The first aspect may be carried out alone or with one or any combinationof the examples of the first aspect discussed above.

In a second aspect, a forming roll comprises a working zone portioncomprising a working zone surface for engaging a stream of molten glass.The working zone surface includes a length extending along a rotationaxis of the forming roll. The forming roll further includes afrustoconical groove defined in the forming roll and extending at anacute angle relative to the rotation axis of the forming roll.

In one example of the second aspect, the frustoconical groove isconfigured such that the working zone surface expands radially from therotation axis in a substantially uniform manner across the length of theworking zone surface as a temperature of the working zone portion isincreased from a first temperature to a second temperature.

In another example of the second aspect, the forming roll furthercomprises a cooling passage configured to provide fluid cooling to theforming roll.

In still another example of the second aspect, the forming roll furthercomprises at least one gap ring mounted to the working zone portion.

In yet another example of the second aspect, the acute angle is fromabout 30° to about 60°.

In another example of the second aspect, the frustoconical grooveextends a depth into the working zone surface that is within a range offrom about 50% to about 85% of a radius of the forming roll.

The second aspect may be carried out alone or with one or anycombination of the examples of the second aspect discussed above.

In a third aspect, a method is provided for forming a glass ribbon withat least one forming roll and a forming body spaced to define a glassforming gap between the forming roll and forming body. The forming rollincludes a working zone portion comprising a working zone surface havinga length extending along a rotation axis of the forming roll. Theforming roll further includes a thermal resistance boundary extending atan acute angle relative to the rotation axis of the forming roll. Themethod comprises the steps of (I) supplying a stream of molten glass and(II) feeding the stream of molten glass through the gap to form a glassribbon including a formed thickness. The thermal resistance boundaryfacilitates substantial uniform radial expansion of the working zonesurface relative to the rotation axis across the length of the workingzone surface in response to heating of the working zone portion by themolten glass.

In one example of the third aspect, the thermal resistance boundary ofstep (II) is provided as a frustoconical end surface of the working zoneportion.

In another example of the third aspect, the thermal resistance boundaryof step (II) is provided as a plurality of bores spaced radially aboutthe rotation axis of the forming roll.

In yet another example of the third aspect, the thermal resistanceboundary of step (II) is provided as a frustoconical groove defined inthe forming roll. For example, the method can include the first step ofstrengthening the frustoconical groove with a plurality of strengthelements positioned within the groove.

In another example of the third aspect, the method further comprises thestep of cooling the forming roll with a fluid. For example, the step ofcooling can include flowing the fluid through a cooling passageextending along the rotation axis of the forming roll. In anotherexample, the step of cooling can include flowing the fluid against aninternal central portion of the forming roll to facilitate substantialuniform expansion of the working zone surface across the length of theworking zone surface in response to heating of the working zone portionby the molten glass.

In another example of the third aspect, the step of directing heat toouter peripheral edges of the working zone portion to facilitatesubstantial uniform expansion of the working zone surface across thelength of the working zone surface in response to heating of the workingzone portion by the molten glass.

In yet another example of the third aspect, the acute angle is fromabout 30° to about 60°.

The third aspect may be carried out alone or with one or any combinationof the examples of the third aspect discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects are better understood when the followingdetailed description is read with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic representation depicting the expansion of twoconventional forming rolls;

FIG. 2 is a perspective view of an example roll forming apparatuscomprising a forming roll spaced from a forming body;

FIG. 3 is an end view of the example roll forming apparatus of FIG. 2;

FIG. 4 is a cross-sectional view of the example roll forming apparatustaken along line 4-4 in FIG. 2;

FIG. 5 is a perspective view of another example forming roll;

FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 5;

FIG. 7 is a side-view of yet another example forming roll;

FIG. 8 is a cross-sectional view along frustoconical planes 8-8 of FIG.7;

FIG. 9 is a perspective view still another example forming roll; and

FIG. 10 is a cross-sectional view along line 10-10 of FIG. 9 showing theforming roll in use.

DETAILED DESCRIPTION

Examples will now be described more fully hereinafter with reference tothe accompanying drawings in which example embodiments are shown.Whenever possible, the same reference numerals are used throughout thedrawings to refer to the same or like parts. However, aspects may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein.

Roll forming apparatus of the disclosure can be useful to produce glassribbon that may be subsequently separated into glass sheets for variousapplications. For example, the glass sheets can be used to manufactureliquid crystal displays (LCDs), electrophoretic displays (EPD), organiclight emitting diode displays (OLEDs), plasma display panels (PDPs) orother devices.

Turning to FIGS. 2-4, one example roll forming apparatus 201 cancomprise a glass feed device 203 for supplying a stream of molten glass205. As shown in FIG. 2, the glass feed device 203 can comprise a fishtail slot feed although other glass feed devices may be provided infurther examples. For instance, the glass feed device can comprise afusion down draw apparatus, a fusion up draw apparatus, a redrawapparatus or other glass feed devices that may supply a stream of moltenglass 205.

As shown, the roll forming apparatus 201 comprises at least one formingroll 207 spaced from a forming body 209. The forming roll and formingbody can comprise various alternative refractory materials (e.g.,ceramic, platinum, etc.). The materials used to manufacture the formingroll and forming body are capable of forming molten glass into a glassribbon while maintaining the structural integrity of the forming rolland forming body. Moreover, as the forming roll and forming body will becontacting the major surfaces of the formed glass ribbon, the formingroll and forming body should be made from a material that will notdamage or otherwise contaminate the major surfaces of the formed glassribbon. For instance, the forming body can be made from various metallicalloys (e.g., stainless steel, nickel alloys).

The forming roll 207 and forming body 209 can define a glass forming gap211 between the forming roll 207 and the forming body 209 for receivingthe stream of molten glass 205. As shown in FIGS. 2-4, the forming body209 can comprise a forming roll that may be identical or different thanthe forming roll 207. Although not shown, further examples may providethe forming body 209 as another member that is not identical or similarto the forming roll 207. For example, the forming body 209 may comprisea member (rotatable or nonrotatable) that may cooperate with the formingroll 207 to define the glass forming gap 211. A glass ribbon 213 can beformed as the stream of molten glass 205 passes through the forming gap211 between the forming roll 207 and forming body 209. The glass ribbon213 can be formed with a thickness T (see FIG. 3) that corresponds to awidth W (see FIG. 4) of the glass forming gap 211.

As shown in FIGS. 2 and 4, the forming roll 207 includes a working zoneportion 215 that comprises a working zone surface 217 for engaging thestream of molten glass 205. The working zone surface 217 may be circularcylindrical although the working zone surface may comprise a polygonalcylindrical configuration or other shaped surface in further examples.Moreover, as shown, the working zone surface 217 has a length Lextending along a rotation axis 219 of the forming roll 207. The formingrolls of the disclosure further include at least one thermal resistanceboundary extending at an acute angle relative to the rotation axis ofthe forming roll. For example, as shown in the figures, the at least onethermal resistance boundary can comprise a first thermal resistanceboundary extending at an acute angle α relative to the rotation axis ofthe forming roll and a second thermal resistance boundary extending ananother acute angle β relative to the rotation axis of the forming roll.As shown, the acute angles α, β may be identical to one another andfacing opposite directions in some examples although the acute anglesmay be different in further examples. The acute angles α, β may have anabsolute value within a range of from about 30° to about 60° althoughother acute angles may be provided in further examples. As shown in FIG.4, providing acute angles α, β that are opposite to one another canprovide the working zone portion 215 with a circumferential dovetailportion between the first thermal resistance boundary and the secondthermal resistance boundary. As further shown in FIG. 4, thecircumferential dovetail portion of the working zone portion 215includes with a trapezoidal cross-sectional portion 401 that is flaredin a radial direction extending away from the rotation axis 219 of theforming roll 207.

As shown in FIG. 4, the first and second thermal resistance boundariesmay be provided at respective end portions 403, 405 of the forming rollto allow heat to be more effectively retained within the working zoneportion 215. Indeed, the thermal resistance boundary provides a locationof relatively higher thermal resistance to heat transfer from theworking zone portion, thereby helping inhibit heat transfer out of theworking zone portion 215 and into the end portions 403, 405 of theforming roll 207. Meanwhile, the angles α, β of the thermal resistanceboundaries can provide desirable thermal distribution characteristics ofthe working zone portion 215. Indeed, by providing the thermalresistance boundary at opposite acute angles α, β relative to therotation axis of the forming roll 207, the illustrated circumferentialdovetail portion with the trapezoidal cross-sectional portion 401 thatis flared in the radial direction extending away from the rotation axis219 of the forming roll 207 may be provided such that heat from thestream of molten glass 205 is retained and appropriately distributedthroughout the working zone portion 215. The resulting heat distributionin the working zone portion 215 provides a desirable temperaturedistribution profile that results in substantial uniform radialexpansion of the working zone surface 217 relative to the rotation axis219 across the length L of the working zone surface 217 in response toheating of the working zone portion 215 by the molten glass 205 from afirst temperature to a second temperature. Due to the substantialuniform radial expansion of the working zone surface 217 during heating,the working zone surface 217 can maintain a substantially uniform radiusacross the length L of the working zone surface 217 throughout heatingand cooling cycles of the forming roll 207.

The thermal resistance boundary may comprise a wide range of alternativeconfigurations. For example, FIG. 4 illustrates a first thermalresistance boundary comprising a first frustoconical groove 407 and asecond thermal resistance boundary comprising a second frustoconicalgroove 409. Each frustoconical groove 407, 409 can be defined in theforming roll 207 to extend at the respective acute angles α, β relativeto the rotation axis 219 of the forming roll 207. The frustoconicalgrooves 407, 409 can extend completely, partially, or intermittentlyaround the circumference of the forming roll 207. For example, as shown,the frustoconical grooves 407, 409 each extend continuously andcompletely about the periphery of the forming roll 207. Providing one orboth of the frustoconical grooves as a continuous frustoconical groovethat extends completely about the periphery of the forming roll canprovide a more efficient boundary to thermal conduction outside theworking zone portion. One or both of the frustoconical grooves mayalternatively comprise discontinuities, such as aligned groove segmentsthat are spaced apart about the periphery of the forming roll 207. Whilethe discontinuities may provide points of reduced thermal resistance,the discontinuities may provide structural integrity to the forming rollthat may not otherwise be achieved by a continuous frustoconical groove.

As further illustrated in FIG. 4, the frustoconical grooves 407, 409 canextend a depth “d” into the working zone surface 217. Various depthranges may be provided to provide a sufficient thermal resistanceboundary while maintaining the structural integrity of the forming roll207. For example, as shown, the forming roll can include a diameter “D”that is twice the radius “R” of the forming roll 207. The depth “d” ofthe frustoconical grooves 407, 409 can be within a range of from about50% to about 85% of the radius “R” of the forming roll 207 althoughother depths may be provided in further examples.

As further shown in FIGS. 2-4, the roll forming apparatus 201 may alsocomprise a pair of gap rings 221, 223, wherein the forming roll 207 andthe forming body 209 are spaced from each other by the pair of gap rings221, 223 to define the glass forming gap 211. While the thermalresistant boundaries of the forming roll 207 and the forming body 209are configured to maintain a substantially uniform width W along lengthL during radial expansion of the forming roll and forming body, the gaprings 221, 223 may be configured to maintain a substantially constantwidth W during this radial expansion. In the example shown in FIGS. 2-4,the gaps rings 221, 223 are mounted to the working zone portion 215 ofthe forming roll 207 and protrude from the working zone surface 217 by adistance X. In alternative examples, one or both of the gap rings 221,223 may be mounted to a working portion 225 of the forming body 209 andprotrude from a working zone surface 227 of the working portion 225 by adistance X. In further examples, as further shown by the gap rings 222,224 in hidden lines in FIG. 2, both the forming roll 207 and the formingbody 209 may each include a pair of gap rings that each extend from thecorresponding working zone surface 217, 227 by a distance X/2.Respective gap rings 221, 222 and 223, 224 can engage one another inoperation such that the total spacing of the working zone surfaces 217,227 provided by the gap rings is X.

Thus, the pair of gap rings 221, 223 can ensure that, during expansion,the working zone surfaces 217, 227 of the forming roll 207 and theforming body 209 will remain separated by a constant width W thatcorresponds to the distance X. Accordingly, a pair of gap rings 221, 223may be selected that protrude from the working zone surface 217 by apredetermined distance X to form a glass ribbon 213 having asubstantially uniform thickness T that corresponds to the predetermineddistance X. As such, thin glass ribbons with a uniform thickness of 1 mmor less can be easily formed without having to predict how the width Wmay change during the expansion of forming rolls absent the use of gaprings. Moreover, even though the gap rings 221, 223 may themselvesexpand as they rise in temperature during the roll forming process, theexpansion of distance X should be nominal when distance X is small (asis the case when forming thin glass sheets of 1 mm or less).Furthermore, the gap rings 221, 223 may be coated with a low thermalconductivity ceramic coating or they may comprise a material having alow coefficient of thermal expansion to reduce the effects of heat onthe expansion of distance X.

The pair of gaps rings 221, 223 may be integral with the forming roll207 and/or forming body 209 or they may be mounted separately to theforming roll 207 and/or forming body 209. Additionally, as discussedabove, there may be a second pair of gap rings (not shown) mounted tothe forming body 209 that contact the first pair of gap rings 221, 223on the forming roll 207. Moreover, although the example provided shows apair of gaps rings 221, 223 mounted on the working zone portion 215 offorming roll 207, they can alternatively be mounted to the end portions403, 405 of the forming roll 207. However, since the working zoneportion 215 will retain heat from the stream of molten glass 205 andtherefore expand at a rate different from (and greater than) the endportions 403, 405, mounting the gap rings 221, 223 on the working zoneportions 215, 225 can lead to a better control of the width W alonglength L. In other words, mounting the gap rings 221, 223 to the endportions 403, 405 will ensure that the end portions 403, 405 remain aconstant distance apart but may not ensure that the working zonesurfaces 217, 227 will remain a constant distance apart since theworking zone surfaces 217, 227 may expand at a rate different from theend portions 403, 405.

As shown in FIG. 4, each of the forming roll 207 and the forming body209 may have a similar (such as the illustrated identical) thermalresistance boundary configuration. In fact, as discussed above, theforming body 209 may be identical to the forming roll 207 such that theforming roll 207 and the forming body 209 form a pair of substantiallyidentical forming rolls as shown. One or both of the forming roll andforming body may have alternative constructions for the thermalresistance boundaries. For example, one or both of the forming roll 207and/or the forming body 209 can comprise the forming roll 501 shown inFIGS. 5 and 6. The forming roll 501 comprises a working zone portion 503comprising a working zone surface 505 for engaging the stream of moltenglass 205. The working zone surface 505 including a length L extendingalong a rotation axis 507 of the forming roll 501. As shown in FIG. 6,the forming roll 501 includes a first thermal resistance boundarycomprising a first frustoconical end surface 601 and a second thermalresistance boundary comprising a second frustoconical end surface 603.Each frustoconical end surface 601, 603 can extend at the respectiveacute angles α, β relative to the rotation axis 507 of the forming roll501.

As further illustrated in FIG. 6, the frustoconical end surfaces 601,603 can extend a depth “d” into the working zone surface 505. Variousdepth ranges may be provided to provide a sufficient thermal resistanceboundary while maintaining the structural integrity of the forming roll503. For example, as shown, the forming roll can include a diameter “D”that is twice the radius “R” of the forming roll 503. The depth “d” ofthe frustoconical end surface 601, 603 can be within a range of fromabout 50% to about 85% of the radius “R” of the forming roll 503although other depths may be provided in further examples.

As shown in FIG. 6, the end surface 601, 603 do not face a correspondingsurface of end portions 605, 607 of the forming roll 501. As such, thethermal resistance boundaries of FIGS. 5 and 6 may have a higher thermalresistance to heat transfer than the thermal resistance boundaries ofFIGS. 2-4. Although not shown, the forming roll 501 may optionallyinclude a plurality of strengthening ribs extending radially about therotation axis 507 and spanning between the end surfaces 601, 603 and therespective end portions 605, 607 to increase the structural strength ofthe forming roll 501.

In further examples, one or both of the forming roll and forming bodycan comprise the forming roll 701 shown in FIGS. 7 and 8. The formingroll 701 comprises a working zone portion 703 comprising a working zonesurface 705 for engaging the stream of molten glass 205. The workingzone surface 705 including a length L extending along a rotation axis707 of the forming roll 701. The forming roll 701 includes a firstthermal resistance boundary comprising a first plurality of bores 709and a second thermal resistance boundary comprising a second pluralityof bores 711. As indicated by the hidden lines 713 of each bore 715, thebores can extend along a bore axis 801 (see FIG. 8) at the respectiveacute angles α, β relative to the rotation axis 707 of the forming roll701 as indicated by frustoconical sectional planes 8-8. FIG. 8illustrates the array of bores 715 radially spaced about the rotationaxis 707 of the forming roll 701 along corresponding frustoconicalplanes 8-8 of FIG. 7. The bores 715 may or may not be equally spacedfrom each other. Additionally, the bores 715 may vary in number, depth,and size from the example shown. In these alternative embodiments, aseach bore axis 801 extends at the respective acute angles α, β, thethermal resistant boundaries similarly extend at acute angles relativeto the rotation axis of the forming roll 701. Providing the thermalresistance boundaries as respective pluralities of bores can provideenhanced structural integrity when compared to other designs that removesubstantial portions of the forming roll to create the thermalresistance boundaries.

In still further examples, one or both of the forming roll and formingbody can comprise the forming roll 901 shown in FIGS. 9 and 10. Theforming roll 901 comprises a working zone portion 903 comprising aworking zone surface 905 for engaging the stream of molten glass 205.The working zone surface 905 including a length L extending along arotation axis 907 of the forming roll 901. The forming roll 901 includesa first thermal resistance boundary comprising a first frustoconicalgroove 909 and a second thermal resistance boundary comprising a secondfrustoconical groove 911. Each frustoconical groove 909, 911 can bedefined in the forming roll 901 to extend at the previously describedrespective acute angles α, β relative to the rotation axis 907 of theforming roll 901. As with the frustoconical grooves 407, 409 illustratedin FIG. 4, the frustoconical grooves 909, 911 can extend completely,partially, or intermittently around the circumference of the formingroll 901. For example, as shown, the frustoconical grooves 909, 911 eachextend completely about the periphery of the forming roll 901. Providingone or both of the frustoconical grooves as a frustoconical groove thatextends completely about the periphery of the forming roll 901 canprovide a more efficient boundary to thermal conduction outside theworking zone portion.

Optionally, one or both of the frustoconical grooves may alternativelycomprise discontinuities to increase the structural integrity of theforming roll that may not otherwise be achieved by the continuousfrustoconical groove. For example, as shown in FIG. 10, each of thefrustoconical grooves 909, 911 may include a plurality of strengthelements, such as the illustrated weld points 1001, 1003, positionedwithin the groove to strengthen the forming roll 901. The weld points1001, 1003 attach the working zone portion 903 to end portions 913, 915of the forming roll 901, thus adding strength and rigidity to theforming roll 901. The weld points 1001, 1003 can extend completely orpartially around the circumference of the forming roll 901. There canalso be more than one weld point positioned within each groove.Moreover, the weld points 1001, 1003 can be positioned radially so thatthey are closer to the surface of the forming roll 901 or they can bepositioned deeper within the grooves so that they are closer to therotation axis of the forming roll 901.

The forming rolls of the disclosure may also include an optional coolingpassage. For example, as shown in FIG. 10, the forming roll 901 includesan optional cooling passage 1007 configured to provide fluid cooling tothe forming roll 901. In some examples, the cooling passage 1007 may becoaxial with the forming roll 901 and extends through the working zoneportion 903. As further illustrated in FIG. 10, the frustoconicalgrooves 909, 911 can extend a depth “d” into the working zone surface905. Various depth ranges may be provided to provide a sufficientthermal resistance boundary while maintaining the structural integrityof the forming roll 903. For example, as shown, the forming roll caninclude a diameter “D” that is twice the radius “R1” of the forming roll903. Moreover, the cooling passage 1007 can include a radius “R2”wherein a wall thickness “WT” is formed between the working zone surface905 and the interior wall surface of the cooling passage 1007. The depth“d” of the frustoconical grooves 909, 911 can be within a range of fromabout 50% to about 85% of the wall thickness “WT” of the forming roll903 although other depths may be provided in further examples.

Cooling fluid may be supplied to this cooling passage 1007 an dispersedas a cooling fluid stream 1009 to cool the forming roll 901 and reduceits expansion during the roll forming process. The cooling fluid may bewater or compressed air or some other cooling fluid. As shown in FIG.10, a conduit 1005 may be provided within the cooling passage 1007 todeliver the cooling fluid and direct the cooling fluid stream 1009against an internal central portion of the forming roll 901.

During the roll forming process, the central portion of the forming roll901 experiences a greater amount of heat than the outer peripheralportions of the forming roll 901. Thus, by directing the cooling fluidtowards the central portion of the forming roll 901, the temperature ofthe central portion can be controlled so that the central portionexpands at a rate substantially uniform to outer peripheral portions ofthe working zone portion 903. Accordingly, directing the fluid stream1009 against an internal central portion of the forming roll 901 canfacilitate substantial uniform expansion of the working zone surface 905across the length L of the working zone surface 905 in response toheating of the working zone portion 903 by the stream of molten glass205.

In addition or in alternative to flowing a cooling fluid through acooling passage, heat H may be directed to outer peripheral edges of theworking zone portion 903 to facilitate substantial uniform expansion ofthe working zone surface 905 across the length L of the working zonesurface 905 in response to heating of the working zone portion 903 bythe molten glass, as shown in FIG. 10. By directing heat towards theouter peripheral edges of the working zone portion 903, the temperatureof the outer peripheral portions can be controlled so that the outerperipheral portions expand at a rate substantially uniform to thecentral portion of the working zone portion 903.

Methods of forming the glass ribbon 213 will now be described and canapply to any of the example forming roll/forming body configurations ofthe disclosure. The method can be carried out with at least one formingroll and a forming body spaced to define a glass forming gap between theforming roll and forming body. As mentioned previously, the forming bodycan comprise various configurations and may be similar or identical tothe forming roll. For example, as shown in FIGS. 2 and 4, both theforming roll 207 and the forming body 209 including working zoneportions 215, 225 comprising the working zone surfaces 217, 227including the length L extending along the rotation axis 219 of thecorresponding forming roll 207 and forming body 209. As mentionedpreviously, the forming roll and forming body can each include thethermal resistance boundary comprising the frustoconical grooves 407,409 defined in the forming roll 207 that each extend at the acute angleα, β relative to the respective rotation axis (e.g., rotation axis 219).The method can provide the acute angles α, β within a range of fromabout 30° to about 60° although other acute angles may be used infurther examples.

As discussed previously, other thermal resistance boundaryconfigurations may be used in further examples. For instance, FIGS. 5and 6 illustrate the thermal resistance boundary comprising thefrustoconical end surface 601, 603 of the working zone portion 503.FIGS. 7 and 8 illustrated another example wherein the thermal resistanceboundary comprises the plurality of bores 709, 711 spaced radially aboutthe rotation axis 707 of the forming roll. As shown in FIGS. 9 and 10,another examples provides the thermal resistance boundary as thefrustoconical groove 909, 911 with the plurality of strength elements(e.g., weld points 1001, 1003) positioned within the groove.

Turning to FIGS. 2 and 3, the methods can further include the steps ofsupplying the stream of molten glass 205 and feeding the stream ofmolten glass through the gap 211 to form the glass ribbon 213 includingthe formed thickness T. The thermal resistance boundary of each exampleof the disclosure facilitates substantial uniform radial expansion ofthe working zone surface relative to the rotation axis across the lengthof the working zone surface in response to heating of the working zoneportion by the molten glass. In one example, the method can furtherinclude the step of cooling the forming roll with a fluid. For instance,as shown in FIG. 10, the method can include flowing the fluid throughthe cooling passage 1007 extending along the rotation axis 907 of theforming roll 901. As further shown, the method can include the step ofcooling by flowing the fluid against the internal central portion of theforming roll, for example, by way of the cooling fluid stream 1009.Flowing the fluid against the internal central portion of the formingroll can facilitate substantial uniform expansion of the working zonesurface 905 across the length L of the working zone surface 905 inresponse to heating of the working zone portion 903 by the molten glass205.

As further shown schematically by “H” in FIG. 10, the method can alsoinclude the step of heating the outer peripheral edges of the workingzone portion 903 to facilitate substantial uniform expansion of theworking zone surface 905 across the length L of the working zone surface905 in response to heating of the working zone portion 903 by the moltenglass 205.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit and scope of the claimed invention.

What is claimed is:
 1. A roll forming apparatus comprising: a glass feeddevice for supplying a stream of molten glass; and at least one formingroll being spaced from a forming body to define a glass forming gapbetween the forming roll and the forming body for receiving the streamof molten glass to form a glass ribbon including a formed thickness,wherein the forming roll comprises a working zone portion comprising aworking zone surface for engaging the stream of molten glass, theworking zone surface including a substantially constant length extendingparallel to a rotation axis of the forming roll with the working zonesurface circumscribing the rotation axis of the forming roll, whereinthe forming roll includes a first thermal resistance boundary extendingtowards the rotation axis of the forming roll at a first acute anglerelative to the rotation axis of the forming roll and a second thermalresistance boundary extending towards the rotation axis of the formingroll at a second acute angle relative to the rotation axis of theforming roll, the first acute angle facing away from the second acuteangle, and the working zone surface being defined between the firstthermal resistance boundary and the second thermal resistance boundary,and wherein the first thermal resistance boundary extending at the firstacute angle and the second thermal resistance boundary extending at thesecond acute angle provide the working zone portion with acircumferential dovetail portion between the first thermal resistanceboundary and the second thermal resistance boundary, and thecircumferential dovetail portion includes a trapezoidal cross-sectionalportion flared in a radial direction extending away from the rotationaxis of the forming roll.
 2. The apparatus of claim 1, wherein the firstthermal resistance boundary and the second thermal resistance boundaryare configured such that the working zone surface expands radially fromthe rotation axis in a substantially uniform manner across the length ofthe working zone surface as a temperature of the working zone portion isincreased from a first temperature to a second temperature.
 3. Theapparatus of claim 1, wherein the first thermal resistance boundarycomprises a first frustoconical end surface of the working zone portionand the second thermal resistance boundary comprises a secondfrustoconical end surface of the working zone portion and thecircumferential dovetail portion is defined between the firstfrustoconical end surface and the second frustoconical end surface. 4.The apparatus of claim 1, wherein at least one of the first thermalresistance boundary and the second thermal resistance boundary comprisesa frustoconical groove defined in the forming roll.
 5. The apparatus ofclaim 4, wherein the frustoconical groove is provided with one or morestrength elements positioned within the groove.
 6. The apparatus ofclaim 1, wherein the forming roll includes a cooling passage configuredto provide fluid cooling to the forming roll.
 7. The apparatus of claim1, further comprising at least one pair of gap rings, wherein theforming roll and forming body are spaced by the pair of gap rings todefine the glass forming gap.
 8. The apparatus of claim 7, wherein thepair of gap rings are mounted to the working zone portion of the formingroll.
 9. The apparatus of claim 1, wherein the first acute angle and thesecond acute angle are each from about 30° to about 60°.
 10. A formingroll comprising: a working zone portion comprising a working zonesurface for engaging a stream of molten glass, the working zone surfaceincluding a substantially constant length extending parallel to arotation axis of the forming roll with the working zone surfacecircumscribing the rotation axis of the forming roll; a firstfrustoconical groove defined in the forming roll, the firstfrustoconical groove extending towards the rotation axis of the formingroll at a first acute angle relative to the rotation axis of the formingroll; and a second frustoconical groove defined in the forming roll, thesecond frustoconical groove extending towards the rotation axis of theforming roll at a second acute angle relative to the rotation axis ofthe forming roll, the first acute angle facing away from the secondacute angle, and the working zone surface being defined between thefirst frustoconical groove and the second frustoconical groove.
 11. Theforming roll of claim 10, wherein the first frustoconical groove and thesecond frustoconical groove are configured such that the working zonesurface expands radially from the rotation axis in a substantiallyuniform manner across the length of the working zone surface as atemperature of the working zone portion is increased from a firsttemperature to a second temperature.
 12. The forming roll of claim 10,further comprising a cooling passage configured to provide fluid coolingto the forming roll.
 13. The forming roll of claim 10, furthercomprising at least one gap ring mounted to the working zone portion.14. The forming roll of claim 10, wherein the first acute angle and thesecond acute angle are from about 30° to about 60°.
 15. The forming rollof claim 10, wherein the frustoconical groove extends a depth into theworking zone surface that is within a range of from about 50% to about85% of a radius of the forming roll.
 16. A roll forming apparatuscomprising: a glass feed device for supplying a stream of molten glass;and at least one forming roll being spaced from a forming body to definea glass forming gap between the forming roll and the forming body forreceiving the stream of molten glass to form a glass ribbon including aformed thickness, wherein the forming roll comprises a working zoneportion comprising a working zone surface for engaging the stream ofmolten glass, the working zone surface including a length extendingalong a rotation axis of the forming roll, wherein the forming rollincludes a thermal resistance boundary comprising a frustoconical groovedefined in the forming roll and extending at an acute angle relative tothe rotation axis of the forming roll, wherein the frustoconical grooveis provided with one or more strength elements positioned within thegroove.
 17. The apparatus of claim 16, wherein the thermal resistanceboundary is configured such that the working zone surface expandsradially from the rotation axis in a substantially uniform manner acrossthe length of the working zone surface as a temperature of the workingzone portion is increased from a first temperature to a secondtemperature.
 18. The apparatus of claim 16, wherein the forming rollincludes a cooling passage configured to provide fluid cooling to theforming roll.
 19. The apparatus of claim 16, further comprising at leastone pair of gap rings, wherein the forming roll and forming body arespaced by the pair of gap rings to define the glass forming gap.
 20. Theapparatus of claim 19, wherein the pair of gap rings are mounted to theworking zone portion of the forming roll.
 21. The apparatus of claim 16,wherein the acute angle is from about 30° to about 60°.
 22. A formingroll comprising: a working zone portion comprising a working zonesurface for engaging a stream of molten glass, the working zone surfaceincluding a length extending along a rotation axis of the forming roll;and a frustoconical groove defined in the forming roll and extending atan acute angle relative to the rotation axis of the forming roll,wherein the frustoconical groove is provided with one or more strengthelements positioned within the groove.
 23. The forming roll of claim 22,wherein the frustoconical groove is configured such that the workingzone surface expands radially from the rotation axis in a substantiallyuniform manner across the length of the working zone surface as atemperature of the working zone portion is increased from a firsttemperature to a second temperature.
 24. The forming roll of claim 22,further comprising a cooling passage configured to provide fluid coolingto the forming roll.
 25. The forming roll of claim 22, furthercomprising at least one gap ring mounted to the working zone portion.26. The forming roll of claim 22, wherein the acute angle is from about30° to about 60°.
 27. The forming roll of claim 22, wherein thefrustoconical groove extends a depth into the working zone surface thatis within a range of from about 50% to about 85% of a radius of theforming roll.
 28. A roll forming apparatus comprising: a glass feeddevice for supplying a stream of molten glass; and at least one formingroll being spaced from a forming body to define a glass forming gapbetween the forming roll and the forming body for receiving the streamof molten glass to form a glass ribbon including a formed thickness,wherein the forming roll comprises a working zone portion comprising aworking zone surface for engaging the stream of molten glass, theworking zone surface including a substantially constant length extendingparallel to a rotation axis of the forming roll with the working zonesurface circumscribing the rotation axis of the forming roll, whereinthe forming roll includes a first thermal resistance boundary extendingtowards the rotation axis of the forming roll at a first acute anglerelative to the rotation axis of the forming roll and a second thermalresistance boundary extending towards the rotation axis of the formingroll at a second acute angle relative to the rotation axis of theforming roll, the first acute angle facing away from the second acuteangle, and the working zone surface being defined between the firstthermal resistance boundary and the second thermal resistance boundary,and wherein at least one of the first thermal resistance boundary andthe second thermal resistance boundary comprises a frustoconical groovedefined in the forming roll.
 29. The apparatus of claim 28, wherein thefrustoconical groove is provided with one or more strength elementspositioned within the groove.